Selection of optimal solution heat treatment of the casting cylinder heads

Abstract

Abstract. The effect of solution treatment on mechanical properties (UTS, elongation, Brinell hardness) and microstructure (Si-morphology and Si-size) of an aluminium alloy (A356) used for casting cylinder heads was studied. The tests were carried out with specimens machined from the bulkheads of V8 engine blocks cast by the low pressure process. The samples were tested in as-cast and T6 heat treating conditions (solution heat treatment at 530°C with different time -2, 3, 4, 5, 6, 7 hours, quenching in water at 20°C and precipitation hardened for 4 hour at 160°C). The results show that used heat treatment improves mechanical properties of the cylinder head casts. Tensile strength and hardness of specimens increase with solution treatment time. The hardness is a reflection of solution strengthening and silicon particle distribution in matrix. Solution temperature 530°C and 5 hours solution time is appropriate to obtain better morphology and distribution of Si particles in microstructure. Prolonged solution treatment (more than 5 hours) leads to a coarsening of the Si particles, while the numerical Si density decreases. As the particle density decreases, a fewer number of sites are available for crack nucleation, and hence, the fracture properties are improved. The data obtained from this study will be used to improve process control, and to help the selection of heat treatment of the casting for future products.

Effect of T6 Heat Treatment on the Microstructure and Hardness of Secondary AlSi9Cu3(Fe) Alloys Produced by Semi-Solid SEED Process

“…These process parameters were selected in order to minimize blistering and residual stresses in the castings after water quenching and to reduce the risk of localised incipient melting of Cu-rich compounds. Moreover, the experimental solution treatments were also chosen in accordance with the conventional solution cycles normally applied in the automotive industry, where shortening the total time is a key issue to increase the productivity and to reduce the manufacturing cost [11][12][13].…”

“…The solution heat treatment leads to the dissolution of intermetallic phases and the spheroidization of eutectic Si with a resulting improvement of alloy ductility [9,10]. The time for solution treatment is strongly dependent on the microstructural scale [10], ranging from few minutes up to several hours [11][12][13]. In general, too short solution treatment does not guarantee that all alloying elements are dissolved in the α-Al matrix and made available for further precipitation hardening; on the contrary, too long solution treatment shows economic limitations because it uses more energy and time than necessary.…”

Optimizing Aging Time to Maximize Hardness and Fatigue Strength of Al-4wt%Cu Alloy

“…Despite this, the reduced number density of β" and Q' (or L) phases, coupled with the presence of coarser θ' precipitates, led to a diminishment in hardness values, particularly in peak-aged conditions at 180 and 220℃. Tillová et al [5] conducted a comprehensive study to evaluate the influence of solution treatment on the microstructure and mechanical properties of an A356 aluminum alloy, commonly used in the casting of cylinder heads. Their research specifically focused on changes in silicon morphology and size, and their effect on the ultimate tensile strength (UTS), elongation, and Brinell hardness of the alloy.…”